Electric braking.



F. W. ALEXANDBRSON.

I ELECTRIC BRAKING.

APPLICATION FILED 00129, 1909.

974,224. Patented Nov. 14910.

MTNEESES: INVERTER 2. 5 5 ERNST E WALE'XANDERS'M .Hirs ATTORNEY nnnsrr'. WQALEXANDEBSON, or SCHENEGTADY, NEW YORK, Assmnonro i E nc'rRIc COMPANY, A CORPORATION or NEW YORK.

nmic'rnrc BRAKING.

. for dynamic braking, and its object is to control.

simplify and to increase the efficiency of the It hasbeen proposed heretofore to operate an alternatmgcurrent commutator motor as a brakinggene'rator by exciting its field with currentapproximately in phase with that of the source and connecting the armaturc to the source, The exciting current may be derived frointhe armature of an exeiter, thefield ofwhich is supplied from thefsource. QSincethe field winding of the exciter s highly inductive, its field current is substantially 90 out of phase with the voltage of the source, and the armature volt- 9.1.1 1 the exciter being in phase with the held current isalso 190 out of phase with the voltage at thesource. This excite'r voltage impressed onthe highly inductive field winding-of the motor produces a. current lagging behind iitt by approximately 90,

and, therefore, approximately in phase with tl efi oltageo fthe source. The excitermay be a machine expressly provided for the purpose, driven either ataconstant speed oryarying inspeed with the motor, or one- 'ot the 'motors of a car equipment may be employedas theexciterfor the other motors. The,connections between the motor armature and the. source areconveniently controlled by meansof a transformer inserted in the consysteii as eter. ism

v a er iatu e11 a peii h gstr neth e pee time n' QtQ thenews nections, the ratio otf. vhich may be varied to vary the. braking ehect.

[In pract ce certal foiiiid in -theoperation'pf such a .,orakingf I have outlined above when a.

ll speed an lining a u is excited with sa'ry, if the motor is to be connected'to the source without an undue rush of current,

Specification of Letters Patent. 5 Application filed octane: 9, 1909. Serial No. 521,924.

v be controlled .in accordance withmy inyen-" d'fliculties have-been. '1

In the drawing, A- represents the armature dfts fieldgt; the proper; phase, i

Patented Nov}; 1910,

be made to the proper taps on" the former between the motor andthe-source. 4

If the motor is connected totaps having :too high or too low a voltage a .rush'of current wi 1 occur between the source and the motor, which may cause a shock on the motor and may cause .burnin of the commutator. Even if the speed c the motor were always constant, each excitationof the motor field would require a certain connection between the motor and the source, and'in practice the motor speed is always constantly varying so-as to complicate the control. r My invention consistsina .novel method of control, whereby the operation is much simplified. I provide means for'yarying si multaneouslythe connections between the source and the motor, and the strength'of current in the motor field for varying the braking torque, and varying independently the strength of the motor field'currenttoad" just the motor armature voltageforfdifien; P

ent speeds. For any iven speed, since the motor connections to t e source and the motor field excitation are controlled and varied simultaneously, the excitation is always of the right amount for each connection of the motor to the source, or, vice versa, each connection of the motor to the "source is necessarily correct for the existing field strength of the motor. Since the motor speed varies,'it is necessary to provide-inde pendent means for adjusting the-motor voltage for different speeds .This' adj ustment" once made, the motor mayq'bezconnectedvtoa any tap of the transformer withoutpro'duc tion. f

of an alternatingcurrent commutator'rhotor;

BI the field, or exciting winding; and G the usual compensatingpwmding.

ofcurrentQ ,wa Since my invention is particularly a pli 'cable to'braking motors or gvehicles, I ve that. the connections frofli'the motor should lindimted the transformer as con.

ing a rush of current,the only etl ectfpro D represents a transformer which-" 'the.n1otor -.may -be connected .to

nected to a supply conductor through a trolley.

E represents the armature and If the field winding of an exciter. This exciter may be a machine provided especially for the purpose, driven either at constant speed or at exciter field F.

H represents a phase controlling device, such as a resistance in the circuit of the exciter field winding.

The primary of transformer G is connected in shunt to the motor armature and compensating winding, so that the voltage impressed on the transformer primary is always the same as that on the motor armature circuit. A contact (Z is connected to one terminal of the motor armature circuit, and by engagementwith difi'erent points on the secondary of transformer D varies the ratio of trailsformation of this transformer. A contact 9 is arranged to vary the number of turns of the secondary of transformer G in circuit with the field winding F, and thereby to adj usttlie voltage impressed on this field winding. This contact g is for the purpose of adjusting the excitation for difi'erent speeds, while the contact d is for the purpose of controlling the braking torque.

Assuming for a moment that the motor is running at a given speed and the contact 9 properly adjusted for that speed, it will be seen that any movement of contact (Z varies the voltage on the motor armature and on the exciter field simultaneously, so that if the transformer G is properly proportioned to give the correct excitation at that certain speed with the contact d in one position, correct excitation will be given with the contact (Z moved to any other position. Consequently, the motor excitation having been adj ustc l for the proper speed, the contact (I may hplaced so as to impress a low voltage both on the motor armature and on the primary of transformer G, and then the contact may be moved so as to increase this voltage and thereby to increase the braking torque, the motor excitation remaining at the proper value for all positions of the contact as long as the motor speed remains constant.

The adjustment of the motor excitation for diti'erent speeds is accomplished, as has been said. by the contact 9. A tachometer may be placed in view of the niotorman, so as to give him information at all times for properly adjusting the contact 1].

The contact 9 is first adjusted in its proper position for the speed at which the motor happens to be running before the motor armature circuit is closed by contact (I. This latter contact is then adjusted to give the desired torque, and if the motor speed is reduced contact 9 may be shifted to maintain the correct excitation while maintaining constant torqueythe contact- (1 remaining fixed, or the torque may be varied by moving this contact.

.In order to simplify the drawi I have omitted the running connections 0 the motor and shown my invention applied to one motor only.' It will be understood that my invention is applicable to any number of motors, and that any suitable running connections may be employed.

I do not wish to he understood as limiting myself to the particular arrangement shown and described, but aim in the appended claims to cover all modifications which come within the scope of my invention.

What I claim new and desire to secure by Letters Patent'of the United States, is

1.. The method of operating an alternating current commiitator motor as a enerator returning energy to the source for dynamic braking, which consists in connecting the motor armature to the source, separately exciting the motor field with current approximately in phase with the voltage of the source, varying simultaneously the connections between the motor armature and the source and the strength of ,the currentsupplied to the motor field to vary the braking torque, and varying the strength of said current independently to'adjust the motor voltage for different speeds.

2. The-method of operating an alternating current commutator motor as a generator returning energy to the source for dynamic braking, which consists in connecting the motor armature to the source through a transformer, separately exciting the motor field with current. approximately in phase with the voltageof the source, varying simultaneously the ratio of transformation of said transformer and the strength of the current supplied to the motor field to vary the braking torque, and varying the strength of said current independently to adjust the motor voltage for different speeds.

3. The method of operating an alternating current commutator motor and an exciter therefor to cause the motor to act as a generator returning energy to the source for dynamic braking, which consists in connecting the exciter armature to the motor field and the motor armature and exciter field to the source, varying sin'mltaneously the connections from the, source to motor armature and exciter field to adjust the braking torque, and varying independently the voltage impressed on the motor field by the exciter' armature to adjust the motor armature voltage for difi'erent speeds.

4. The method of operating an alternating current commutator motor and an excitertherefor to cause the motor to act as a tionally the motor armature and cxciter field to var the braking torque, and varying independently the Volta e impressed from the source on the exciter old to adjust the motor armature voltage for different speeds.

5. In combination with an alternating current commutator motor and a source of current therefor, means for supplying to the motor field a current approximately in phase with the voltage ofthe source, means or connecting the motor armature to the source and for "arying simultaneously the connections between the motor armature and.

the source and the strength of current supplied to the motor field, and inde endent.

means for varying the stren h of said current.

6. n combination with an alternating independent y A current commutator motor and a source of current therefor, a transformer, means for supplying to the motor field a current approximately in phase with the voltage of the source, means for connecting the motor to the source through said transformer and for varying simultaneously the ratio of transformation of said transformer and the strength of the current supplied to the mo tor field, and i "dependent means for varying independen ly the strength ofsaid current.

7. In combination with an alternating current commutator motor and a source of current therefor, a transformer, an exciter for the field of said motor, means for con necting the eXciter field and the motor. ar-

former and for .vary'in the ratio of transformation of said trans ormer so as to affect the motor armature and exciter field SlIIlllltane'ously, and independent means for vary,-

ing the voltage impressed by said exciter on the motor field.

8. In combination with an alternating current commutator motor anda source of current therefor, a transformer, an .-exciter for the field of said motor, means for connecting the exciter field and the motor at.- mature to the source. through said transformer and for varyin the ratio of transformation of said trans ormer so as to affect the motor armature and egciter field simul mature to the source through said trans- I taneously, and independentmeans for varying the voltage impressed from said source on the exciter field.

In witness whereof, I have hereunto set my hand this 8th day of October, 1909.

ERNST F. W. ALEXANDERSO'N.

Witnesses:

BENJAMIN B. HULL, 'H'ELEN Ommnn. 

